Along with the thinning of portable electronic devices, a speaker module as an important acoustic device also becomes increasingly thinner. Usually, the speaker module comprises a front acoustic cavity and a rear acoustic cavity, where the front acoustic cavity refers to an acoustic cavity formed of the space above the diaphragm in the speaker module, while the rear acoustic cavity refers to an acoustic cavity formed of the space below the diaphragm in the speaker module. Usually, the volume of the front acoustic cavity is not necessary to be large, however, in order to enhance the acoustic characteristics in the low frequency of the speaker module, the volume of the rear acoustic cavity is required to be relatively large. Along with the thinning of the speaker module, the space left to the rear acoustic cavity becomes smaller and smaller, and thus it is difficult to guarantee the acoustic performance of the speaker module while implementing the thinning of the speaker module. Therefore, it is necessary to improve the structure of the speaker module, so as to reduce the impact of the thinning of the speaker module on its acoustic characteristics (particularly those in the low frequency).